Microwave plasma processing apparatus

ABSTRACT

In a microwave plasma processing apparatus, when a surface of a planar antenna  31  for radiating a microwave to form a plasma is concentrically divided into a central region  31   a,  an outer circumferential region  31   c  and a middle region  31   b  therebetween, a plurality of pairs of microwave radiating holes  32  elongated in different directions are concentrically arranged in the central region  31   a  and the outer circumferential region  31   c  and no microwave radiating hole is formed in the middle region  31   b,  and a microwave radiating surface of a microwave transmitting plate  28  is provided with a concave portion  28   a.

TECHNICAL FIELD

The present invention relates to a microwave plasma processing apparatus for executing a plasma process such as an oxidizing process or nitriding process.

BACKGROUND

A plasma process is an indispensable technique for manufacturing a semiconductor device. With an ongoing need for higher integration and higher speed LSI, a semiconductor device including an LSI has been designed to be more and more miniaturized. At the same time, the size of a semiconductor wafer has been enlarged. In accordance with foregoing, there is a need for a plasma processing apparatus suitable for the miniaturized semiconductor device and the enlarged semiconductor wafer.

However, a conventional plasma processing apparatus such as a parallel-plate type or an inductive-coupling type is likely to cause plasma damage to fine devices due to high electron temperature. In addition, a limited area of higher plasma density makes it difficult to uniformly and promptly use a plasma-process on a large-sized semiconductor wafer.

Thus, an RLSA (Radial Line Slot Antenna) microwave plasma processing apparatus, which is capable of uniformly forming a plasma of a higher density and a lower electron temperature, has been considered (for example, WO 2004/008519).

In the RLSA microwave plasma processing apparatus, a planar antenna (Radial Line Slot Antenna) having a number of slots in a predetermined pattern is installed on an upper part of a chamber to radiate a microwave induced from a microwave source into the chamber, which is maintained in a vacuum state, through slots (radiating holes) of the planar antenna and a microwave transmitting plate of dielectric materials disposed below the planar antenna. A gas introduced into the chamber is plasma-processed in the electric field of the microwave. A workpiece such as a semiconductor wafer is processed by the thus generated plasma.

The RLSA microwave plasma processing apparatus provides a high plasma density over a wide area directly below the antenna, so that a uniform plasma process can be executed in a short period of time. Further, since a plasma of a low electron temperature is formed, the semiconductor device is less damaged.

Using such an advantage of less damage and high uniformity, this RLSA microwave plasma processing apparatus has been considered to be applied to various processes such as an oxidizing process or nitriding process.

In such a microwave plasma processing apparatus, a microwave generated from a microwave generating source is guided through a waveguide to the planar antenna having a plurality of slots (radiating hole). Then, the microwave is propagated from a central portion of the planar antenna toward a peripheral portion. During this propagation, a circular-polarized microwave is radiated from a plurality of the slots through the microwave transmitting plate of the dielectric materials into the chamber. The microwave electric field formed by the radiated microwave generates a plasma of the gas introduced into the chamber.

In the above document, the slots of the planar antenna are uniformly formed and the microwave transmitting plate is flatly formed to provide a uniform plasma. However, the microwave is transmitted from the slot through the microwave transmitting plate made of the dielectric materials and radiated into the chamber while being propagated from the central portion of the planar antenna toward the peripheral portion. Thus, due to a reflected wave generated while transmitting the microwave through the microwave transmitting plate made of the dielectric materials, the microwave is not uniformly introduced into the chamber and the electric field strength is not necessarily uniform, for example, the electric field strength on the central portion becomes higher than that at the peripheral portion. Thus, there may be a case where a required uniformity of the plasma is not obtained. Further, efficiency of the microwave cannot be necessarily sufficient.

SUMMARY

An object of one embodiment of the present invention is to provide a microwave plasma processing apparatus capable of uniformly radiating a microwave, forming a plasma of high uniformity and efficiently introducing microwave power.

According to a first aspect of the present invention, provided is a microwave plasma processing apparatus for forming a plasma of a process gas by a microwave and executing a plasma process to a workpiece by the plasma, comprising: a chamber in which the workpiece is housed; a placing table for placing the workpiece in the chamber; a microwave generating source for generating a microwave; a waveguide for guiding the microwave generated from the microwave generating source toward the chamber; a planar antenna made of a conductive material for radiating the microwave guided by the waveguide toward the chamber; a microwave transmitting plate made of a dielectric material, the microwave transmitting plate defining a top wall of the chamber and transmitting the microwave that has passed through microwave radiating holes of the planar antenna; and a process gas supply unit for supplying the process gas into the chamber. The planar antenna has a plurality of microwave radiating holes elongated in one direction. When a surface of the planar antenna is concentrically divided into a central region, an outer circumferential region and a middle region therebetween, a plurality of pairs of the microwave radiating holes elongated in different directions are concentrically arranged in the central region and the outer circumferential region and no microwave radiating hole is formed in the middle region. A concave portion is formed in a microwave radiating surface of the microwave transmitting plate.

In the first aspect of the present invention, the concave portion is formed in a portion corresponding to the workpiece placed in the placing table. Further, the microwave transmitting plate has an arch-type cross-section. Also, a portion corresponding to the concave portion of the microwave transmitting plate is flat.

According to a second aspect of the present invention, provided is a microwave plasma processing apparatus for forming a plasma of a process gas by a microwave and executing a plasma process to a workpiece by the plasma, comprising: a chamber in which the workpiece is housed; a placing table for placing the workpiece in the chamber; a microwave generating source for generating a microwave; a waveguide for guiding the microwave generated in the microwave generating source toward the chamber; a planar antenna made of a conductive material for radiating the microwave guided by the waveguide toward the chamber; a microwave transmitting plate made of a dielectric material, the microwave transmitting plate defining a top wall of the chamber and transmitting the microwave that has passed through microwave radiating holes of the planar antenna; and a process gas supply unit for supplying the process gas into the chamber. The planar antenna has a plurality of microwave radiating holes elongated in one direction. When a surface of the planar antenna is concentrically divided into a central region, an outer circumferential region and a middle region therebetween, a plurality of pairs of the microwave radiating holes elongated in different directions are concentrically arranged in the central region and the outer circumferential region and no microwave radiating hole is formed in the middle region. A microwave radiating surface of the microwave transmitting plate is formed in a concavo-convex shape.

In the second aspect, the convex portions and concave portions are concentrically formed by turns in the microwave radiating surface of the microwave transmitting plate.

In the first and second aspects, it is preferred that the pair of the microwave radiating holes is formed such that ends elongated in a longitudinal direction are close to each other and the other ends are spaced from each other. It is preferred that an angle formed between the longitudinal directions of each microwave radiating hole of the pair of the microwave radiating holes ranges from 80° to 100°. Further, a length along the longitudinal direction of the microwave radiating hole formed in the central region is shorter than a length along the longitudinal direction of the microwave radiating hole formed in the outer circumferential region. Also, the microwave radiating surface of the microwave transmitting plate may have annular projections in its periphery projected downwardly.

According to the present invention, when the surface of the planar antenna radiating the microwave is concentrically divided into the central region, the outer circumferential region and the middle region therebetween, it is configured so that a plurality of pairs of the microwave radiating holes elongated in different directions are concentrically arranged in the central region and the outer circumferential region and no microwave radiating hole is formed in the middle region. Further, it is configured that the microwave radiating surface of the microwave transmitting plate is provided with the concave portions or formed in a concavo-convex shape. Thus, when the microwave is propagated from the central portion toward the peripheral portion of the microwave transmitting plate and then transmitted from the microwave radiating holes through the microwave transmitting plate and thus radiated into the chamber, the microwave can be efficiently and uniformly radiated by minimizing a standing wave or a reflected wave to thereby form a plasma of high uniformity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a microwave plasma processing apparatus in accordance with one embodiment of the present invention.

FIG. 2 shows a planar antenna used in the microwave plasma processing apparatus of FIG. 1.

FIG. 3A shows one embodiment of a concave portion formed in the microwave transmitting plate.

FIG. 3B shows another embodiment of a concave portion formed in the microwave transmitting plate.

FIG. 3C shows another embodiment of a concave portion formed in the microwave transmitting plate.

FIG. 3D shows another embodiment of a concave portion formed in the microwave transmitting plate.

FIG. 3E shows another embodiment of a concave portion formed in the microwave transmitting plate.

FIG. 4 shows a portion of a gas supply system of a microwave plasma processing apparatus in accordance with another embodiment of the present invention.

FIG. 5A shows a position where an electric field strength distribution of FIG. 6A is obtained.

FIG. 5B shows a position where an electric field strength distribution of FIG. 6B is obtained.

FIG. 6A shows an electric field strength distribution of a lower surface of an arch portion when a microwave transmitting plate having an arch-type cross-section is used.

FIG. 6B shows an electric field strength distribution of a lower surface when a flat-type microwave transmitting plate is used.

FIG. 7A shows a position where an electric field strength distribution of FIG. 8A is obtained.

FIG. 7B shows a position where an electric field strength distribution of FIG. 8B is obtained.

FIG. 8A shows an electric field strength distribution from an upper surface of the microwave transmitting plate to a portion being 30 mm lower from the upper surface when the microwave transmitting plate having the arch-type cross-section is used.

FIG. 8B shows an electric field strength distribution from an upper surface of the microwave transmitting plate to a portion being 30 mm lower from the upper surface when the flat-type microwave transmitting plate is used.

FIG. 9 shows an electron density distribution of an oxidizing plasma in each microwave power when the flat-type microwave transmitting plate is used.

FIG. 10 shows an electron density distribution of the oxidizing plasma in each microwave power when the microwave transmitting plate having the arch-type cross-section is used.

FIG. 11 shows an electron density distribution of a nitriding plasma in each microwave power when the flat-type microwave transmitting plate is used.

FIG. 12 shows an electron density distribution of the nitriding plasma in each microwave power when the microwave transmitting plate having the arch-type cross-section is used.

FIG. 13 is a partial cross-sectional view of a microwave plasma processing apparatus in accordance with another embodiment of the present invention.

FIG. 14 is a bottom view of a microwave transmitting plate of FIG. 13.

FIG. 15 is a partial cross-sectional view of a microwave plasma processing apparatus in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION

An embodiment of the present invention will be specifically described below, with reference to the attached drawings.

FIG. 1 is a schematic cross-sectional view of a microwave plasma processing apparatus in one embodiment according to the present invention. The microwave plasma processing apparatus is configured as an RLSA (Radial Line Slot Antenna) microwave plasma processing apparatus capable of generating a microwave plasma of high density and lower electron temperature by introducing a microwave into a processing chamber by a planar antenna, in particular, an RLSA having a plurality of slots and thus generating a plasma.

A plasma processing apparatus 100 has a substantially cylindrical chamber 1 which is sealed and grounded. A circular opening 10 is formed in a central portion of a bottom wall 1 a of the chamber 1. The bottom wall 1 a is provided with an exhaust chamber 11, which is communicated with the opening 10 and extended downwardly.

The chamber 1 includes a susceptor 2 made of ceramics such as AlN for horizontally supporting a semiconductor wafer W (hereinafter, “wafer”) which is a substrate to be processed. The susceptor 2 is supported by a cylindrical support member 3, which is made of ceramics such as AlN, extending upwardly from a bottom center of the exhaust chamber 11. A guide ring 4 for guiding the wafer W is disposed on an outer edge portion of the susceptor 2. Further, an electrical resistance heater 5 is embedded in the susceptor 2. The heater 5 is turned on by a heating power source 6 to thereby heat the susceptor 2 and heat the wafer W with the heat of the susceptor 2. At this time, for example, a process temperature is controllable ranging from room temperature to 800° C. Further, a cylindrical liner 7 made of high purity quartz having less impurities is disposed on an inner periphery of the chamber 1. The liner 7 prevents contamination of metals to establish a clean circumstance. Further, in order to uniformly exhaust the chamber 1, a baffle plate 8, which is made of high purity quartz having less impurities, having a number of exhaust holes 8 a is annularly disposed. The baffle plate 8 is supported by a plurality of braces 9.

The susceptor 2 is provided with wafer support pins (not shown) for supporting and vertically moving the wafer W. The pins are projectable and retractable relative to a surface of the susceptor 2.

On a side wall of the chamber 1, an annular gas introduction member 15 is disposed and gas emitting holes are uniformly formed. A gas supply unit 16 is connected to the gas introduction member 15. The gas introduction member may be arranged like a shower. The gas supply unit 16 has, for example, an Ar gas supply source 17, an O₂ gas supply source 18 and an H₂ gas supply source 19. These gases are transferred via each gas line 20 to the gas introduction member 15 and uniformly introduced into the chamber 1 from the gas emitting holes of the gas introduction member 15. Each gas line 20 is provided with a mass flow controller 21 and an opening/closing valve 22 before and after the mass flow controller 21. Further, instead of Ar gas, other rare gases such as Kr, He, Ne, Xe and the like may be used or no rare gas may be used as explained below.

An exhaust pipe 23 is connected to a side surface of the exhaust chamber 11. An exhaust device 24 including a high speed vacuum pump is connected to the exhaust pipe 23. When the exhaust device 24 is activated, a gas in the chamber 1 is uniformly discharged into a space 11 a of the exhaust chamber 11 and then discharged via the exhaust pipe 23. Thus, the inside of the chamber 1 can be promptly depressurized to a predetermined vacuum degree, e.g., 0.133 Pa.

The side wall of the chamber 1 is provided with a loading/unloading port 25 for loading and unloading the wafer W between a transfer chamber (not shown) adjacent the plasma processing apparatus 100, and a gate valve 26 for opening and closing the loading/unloading port 25.

An upper portion of the chamber 1 is formed as an opening. A lid 27 is disposed on the opening so as to be projected along a peripheral portion and the projected part is a ring-shaped support portion 27 a. A microwave transmitting plate 28 made of dielectric materials, e.g., ceramics such as quartz or Al₂O₃ or AlN is disposed on the ring-shaped support portion 27 a and sealed by a sealing member 29. The microwave transmitting plate 28 transmits a circular polarized microwave radiated from microwave radiating holes (slots) 32 of a planar antenna 31 which will be explained below. Thus, the inside of the chamber 1 is kept sealed. The microwave is transmitted through the microwave transmitting plate 28 and radiated into the chamber 1 to generate an electromagnetic field. A concave portion 28 a is formed at a central portion of a microwave radiating surface of a lower surface of the microwave transmitting plate 28. The concave portion 28 a has an arch-type cross-section and a diameter of the concave portion 28 a is larger than a diameter of the wafer W. Further, a portion of the concave portion 28 a corresponding to the wafer W is flat. A thickness of the portion of the microwave transmitting plate 28 in the portion corresponding to the concave portion 28 a is in some embodiments equal to or lower than ¼×λg (λg: in-pipe wavelength of the microwave). For example, when the microwave is 2.45 GHz, the thickness in some embodiments ranges from 10 to 30 mm ( 1/10×λg to ¼×λg). Further, a height of the concave portion 28 a ranges in some embodiments from 15 to 25 mm (⅛×λg to ⅕×λg).

A disc-type planar antenna 31 is disposed above the microwave transmitting plate 28 to face the susceptor 2. The planar antenna 31 is engaged with an upper portion of the side wall of the chamber 1. The planar antenna 31 has a diameter slightly larger than the microwave transmitting plate 28. The planar antenna 31 is a disc made of conductive materials having a thickness, in some embodiments, ranging from 0.1 to several mm (for example, 1mm) such as copper, aluminum or Ni with its surface plated with gold or silver. The planar antenna 31 is penetrated with a plurality of the microwave radiating holes (slots) 32 in a predetermined pattern.

Specifically, as shown in FIG. 2, the microwave radiating hole 32 is elongated in one direction. Two microwave radiating holes 32 elongated in different directions make a pair, and the circular polarized microwave is radiated from the pair of the microwave radiating holes 32. When a surface of the planar antenna 31 is concentrically divided into a central region 31 a, an outer circumferential region 31 c and a middle region 31 b therebetween, a plurality of the pairs of the microwave radiating holes 32 are concentrically arranged in the central region 31 a and the outer circumferential region 31 c and no microwave radiating hole 32 is formed in the middle region 31 b. When a distance between a center point of the microwave radiating hole 32 at an inner side of the central region 3 la and a center of the planar antenna 31 is set as “1,” a distance between a center point of the microwave radiating hole 32 at an inner side of the outer region and the center of the planar antenna 31 in some embodiments ranges from 2 to 4 and can in some instances be 2.58.

The pair of the microwave radiating holes 32 is formed such that ends extending in a longitudinal direction are close to each other and the other ends are spaced from each other, and an angle formed between the longitudinal directions in FIG. 2 in some embodiments ranges from 80° to 100° and in other embodiments ranges from 85° to 95°. Further, in FIG. 2, the microwave radiating hole 32 has an angle of approximately 45° to a line passing from the center of the planar antenna 31 to a center of the microwave radiating hole 32 in its longitudinal direction. This angle, in some embodiments, ranges from 40° to 50°. Further, a length along the longitudinal direction of the microwave radiating hole 32 formed in the central region 31 a is shorter than a length along the longitudinal direction of the microwave radiating hole 32 formed in the outer circumferential region 31 c. The pairs of the microwave radiating holes 32 in the outer circumferential region 31 c and the central region 31 a are arranged using the same interval. In this embodiment, twenty-four pairs of the microwave radiating holes 32 are formed in the outer circumferential region 31 c and six pairs of the microwave radiating holes 32 are formed in the central region 31 a. However, the number of the microwave radiating holes is not specifically limited but may be determined depending on the required properties.

As to a positional relationship between the concave portion 28 a of the microwave transmitting plate 28 and the microwave radiating hole 32, the concave portion 28 a in some embodiments is engaged with at least a portion of the microwave radiating hole 32 at the inner side of the pair of the microwave radiating holes 32 formed in the outer circumferential region 31 c. This may enhance the electric field strength on a lower surface of the portion of the microwave transmitting plate 28 corresponding to the concave portion 28 a.

A slow-wave member 33 is disposed on an upper surface of the planar antenna 31. The slow-wave member 33 is made of resins having a dielectric constant larger than vacuum such as quartz, polytetrafluoroethylene, polyimide and the like. The slow-wave member 33 has a function of adjusting the plasma by shortening a wavelength of the microwave since the wavelength of the microwave becomes longer in vacuum. The planar antenna 31 and the microwave transmitting plate 28, and the slow-wave member 33 and the planar antenna 31 are closely arranged to each other. However, they may be spaced from each other. Since the reflected wave can be restrained by an arrangement of the slots 32 in the planar antenna 31 and the slow-wave member 33, the efficiency of introducing the microwave can be increased.

A cover member 34 is disposed on an upper surface of the chamber 1 so as to cover the planar antenna 31 and the slow-wave member 33. The cover member 34 is made of metallic materials such as aluminum, stainless steel, copper and the like and functions as a waveguide. The upper surface of the chamber 1 and the cover member 34 are sealed by a sealing member 35. The cover member 34 is provided with a cooling water passage 34 a, which is configured to cool the cover member 34, the slow-wave member 33, the planar antenna 31 and the microwave transmitting plate 28 by allowing a coolant to flow therethrough. Thus, the microwave transmitting plate 28, the planar antenna 31, the slow-wave member 33 and the cover member 34 are prevented from being deformed or damaged by the heat of the plasma. The cover member 34 is grounded.

An opening 36 is formed in a center of an upper wall of the cover member 34 and connected with a waveguide 37. A microwave generating unit 39 is connected to an end of the waveguide 37 via a matching circuit 38. Thus, a microwave having a frequency of, e.g., 2.45 GHz generated from the microwave generating unit 39 is transferred to the planar antenna 31 via the waveguide 37. The microwave may have a frequency of 8.35 GHz or 1.98 GHz.

The waveguide 37 includes a coaxial waveguide 37 a having a circular cross-section, which extends upwardly from the opening 36 of the cover member 34, and a rectangular waveguide 37 b extending horizontally, which is connected to an upper end of the coaxial waveguide 37 a via a mode converter 40. The mode converter 40 between the rectangular waveguide 37 b and the coaxial waveguide 37 a has a function of converting the microwave propagating within the rectangular waveguide 37 b from a TE mode into a TEM mode. An inner conductor 41 made of metallic materials such as stainless steel (SUS), copper, aluminum and the like extends to a center of the coaxial waveguide 37 a. A lower end of the inner conductor 41 is inserted into a hole 31 d formed in the center of the planar antenna 31 and fixed by a screw from an opposite side. Thus, the microwave propagates uniformly and efficiently via the inner conductor 41 of the coaxial waveguide 37 a to a flat waveguide formed by the planar antenna 31 and the cover member 34, thereby being transmitted from the microwave radiating holes 32 of the planar antenna 31 through the microwave transmitting plate 28 and uniformly radiated into the chamber 1.

Each part of the microwave plasma processing apparatus 100 is configured to be connected to and controlled by a process controller 50 provided with a microprocessor (computer). A user interface 51 and a storage unit 52 are connected to the process controller 50. The user interface 51 includes a keyboard, through which an operator executes an input operation of a command in order to manage the plasma processing apparatus 100, and a display for visualizing and displaying operating situations of the plasma processing apparatus 100. The storage unit 52 stores recipes, that is, a control program for embodying various processes executed in the plasma processing apparatus 100 by controlling the process controller 50 or a program for executing processes in each part of the plasma processing apparatus 100 depending on process conditions. The recipes are stored in a storage medium within the storage unit 52. The storage medium may include a hard disc, a semiconductor memory, or a potable device such as CD-ROM, DVD, a flash memory and the like. Further, the recipes may be appropriately transferred from other devices via a dedicated line, for example.

If necessary, a given recipe is called from the storage unit 52 by an instruction from the user interface 51 and executed in the process controller 50. Thus, under control of the process controller 50, a desired process in the plasma processing apparatus 100 is executed.

Next, an operation for executing a plasma oxidizing process by the plasma processing apparatus configured as above will be explained.

First, the gate valve 26 is open. The wafer W to be oxidized is carried into the chamber 1 through a port 25 and then loaded on the susceptor 2.

Then, from the Ar gas supply source 17 and the O₂ gas supply source 18 of the gas supply system 16, Ar gas and O₂ gas are introduced with a predetermined flow rate via the gas introduction member 15 into the chamber 1 under a predetermined process pressure. The process pressure in the chamber 1 ranges, for example, from 6.7 to 677 Pa. Further, a ratio of oxygen in the process gas (flow rate ratio, that is, volume ratio) ranges from 0.1 to 100%. The flow rate of the process gas ranges, for example, from 0 to 5000 mL/min for Ar gas and from 1 to 1000 mL/min for O₂ gas.

Further, in addition to Ar gas and O₂ gas from the Ar gas supply source 17 and the O₂ gas supply source 18, H₂ gas may be introduced from the H₂ gas supply source 19 with a predetermined ratio. By supplying H₂ gas, an oxidizing rate in the plasma oxidizing process can be improved. This is because an OH radical generated by supplying H₂ gas contributes an oxidizing rate improvement. In some embodiments, a ratio of H₂ ranges from 0.1 to 10% of a total amount of the process gas. Further, in some embodiments, a flow rate of H₂ gas ranges from 1 to 500 mL/min (sccm).

The process temperature may range from 200 to 800° C. and, in some embodiments, range from 400 to 600° C.

Continuously, the microwave from the microwave generating unit 39 is guided to the waveguide 37 via the matching circuit 38. The microwave passes through the rectangular waveguide 37 b, the mode converter 40 and the coaxial waveguide 37 a, and then is supplied to the planar antenna 31. The microwave is transferred through the rectangular waveguide 37 b in the TE mode. The microwave is converted from the TE mode into the TEM mode by the mode converter 40 and transferred through the coaxial waveguide 37 a toward the flat waveguide formed by the planar antenna 31 and the cover member 34. The microwave radiates a circular polarized wave by passing the pair of the microwave radiating holes 32 of the planar antenna 31. The circular polarized wave is transmitted through the microwave transmitting plate 28, and radiates to an upper space of the wafer W within the chamber 1. In some embodiments, the power of the microwave generating unit 39 ranges from 0.5 to 5 kW (0.2 to 2.5 W/cm²).

Since the microwave is radiated from the planar antenna 31 via the microwave transmitting plate 28 into the chamber 1, the electromagnetic field is generated in the chamber 1 and Ar gas and O₂ gas are plasma-processed, so that a silicon surface of the wafer W is oxidized by this plasma. This microwave plasma becomes a plasma of high density of approximately 1×10¹⁰ to 5×10¹²/cm³ or more in some embodiments since the microwave is radiated from a number of the microwave radiating holes 32 of the planar antenna 31, and the electron temperature of the plasma is as low as 0.5 to 2 eV and lower around the wafer as 1.1 eV or less. Thus, it is advantageous that since damage to an oxide film by ions in the plasma is decreased due to the plasma of the low electron temperature, a superior silicon oxide film can be obtained.

The microwave is propagated from the central portion of the planar antenna 31 toward the peripheral portion and transmitted from a plurality of the slots 32 through the microwave transmitting plate 28 made of the dielectric materials and the circular polarized microwave is radiated into the chamber 1. Due to a reflected wave generated when the microwave is transmitted through the microwave transmitting plate 28 made of the dielectric materials, the microwave is not uniformly introduced into the chamber and the electric field strength within the dielectric becomes non-uniform, for example, the electric field strength on the central portion becomes higher than that on the peripheral portion. Therefore, a required uniformity of the plasma may not be obtained, so that the uniform plasma process is not necessarily executed. Thus, in some embodiments, a thickness uniformity of the oxide film becomes about 5%.

Therefore, in the present embodiment, the planar antenna 31 is configured as shown in FIG. 2 such that when the surface of the planar antenna 31 is concentrically divided into the central region 31 a, the outer circumferential region 31 c and the middle region 31 b therebetween, a plurality of the pairs of the microwave radiating holes 32 for radiating the circular polarized microwave are concentrically arranged in the central region 31 a and the outer circumferential region 31 c and no microwave radiating hole 32 is formed in the middle region 31 b. Thus, when the microwave is propagated from the central portion of the microwave transmitting plate 28 toward the peripheral portion and radiated from the microwave radiating holes 32, the microwave can be uniformly radiated. Since the microwave radiating surface of the microwave transmitting plate 28 is provided with the concave portion 28 a, a thickness of the central portion of the microwave transmitting plate 28 becomes thinner to restrain a generation of the reflected wave and thus be capable of effectively radiating the microwave, and the uniform microwave from the slots 32 of the planar antenna 31 can be radiated while maintaining the uniformity. Thus, the electric field strength of the microwave radiating surface of the microwave transmitting plate 28 can be higher and uniform, so that an in-plane uniformity of a plasma strength can be enhanced. In particular, the concave portion 28 a has an arch-type cross-section. The diameter of the concave portion 28 a is larger than the diameter of the wafer W. The portion of the concave portion 28 a corresponding to the wafer W is flat. Therefore, the electric field is uniformly formed in the portion corresponding to the wafer W and the electric field is also supplied from a lateral direction of the wafer W. Thus, the uniformity of the electric field strength on the surface of the wafer W is enhanced.

Since the pair of the microwave radiating holes 32 formed in the planar antenna 31 is configured such that ends elongated in the longitudinal direction of each microwave radiating hole 32 are close to each other and the other ends are spaced from each other, the microwave power can be efficiently and uniformly introduced into the chamber 1. By forming the angle between the pair of the microwave radiating holes in the longitudinal direction to be established as ranging from 80° to 100° in some embodiments, and in other embodiments ranging from 85° to 95°, for example, around 90°, the power efficiency and uniformity of the microwave introduced into the chamber 1 can be further enhanced. By disposing the microwave radiating hole 32 to be inclined with the angle of approximately 45° to the line passing from the center of the planar antenna 31 to the center of the microwave radiating hole 32, the power efficiency and uniformity of the microwave introduced into the chamber 1 can be further enhanced likewise. Also, by adjusting the length of the microwave radiating hole 32 formed in the central region 31 a to be shorter than the length of the microwave radiating hole 32 formed in the outer circumferential region 31 c, the power efficiency and uniformity of the microwave introduced into the chamber 1 can be further enhanced.

In the above embodiment, the concave portion 28 a is configured to have an arch-type cross-section. However, the present invention is not limited to such configuration, but may include various concave portions such as a concave portion 28 b having a mountain-type cross-section shown in FIG. 3A, a concave portion 28 c having a trapezoid-type cross-section shown in FIG. 3B, a concave portion 28 d having a rectangular cross-section shown in FIG. 3C, a concave portion 28 e having steps shown in FIG. 3D, and a concave portion 28 f having a dome-type cross-section shown in FIG. 3E.

Next, another embodiment of the present invention will be explained.

The microwave plasma processing apparatus for executing the oxidizing process has been explained above. The microwave plasma processing apparatus in the present embodiment executes a nitriding process instead of the oxidizing process. FIG. 4 shows a portion of a gas supply system of a microwave plasma processing apparatus in the present embodiment. As shown in FIG. 4, instead of the gas supply system 16, the present embodiment includes a gas supply system 16′ having an Ar gas source 17′ and an N₂ gas source 18′ to supply Ar gas and N₂ gas, respectively, into the chamber 1 and form a microwave plasma of nitrogen to execute a nitriding process. Except the above configuration, other features are similar to FIG. 1. Conditions for the nitriding process are as follows: a temperature ranges from 300 to 800° C.; a pressure in the chamber 1 ranges from 1.3 to 133 Pa; a flow rate of Ar gas ranges from 0 to 5000 mL/min; and a flow rate of N₂ gas ranges from 1 to 1000 mL/min.

Below will be explained results of a simulation of the microwave plasma processing apparatus using the planar antenna shown in FIG. 2 and the flat type microwave transmitting plate and the microwave transmitting plate having an arch-type cross-section shown in FIG. 1. Conditions are as follows. The simulation allows the electron density of the plasma to range from 5 to 9×10¹⁰/cm³ around the lower surface of the microwave transmitting plate and the electron density of the plasma to be 1×10¹²/cm³ at a position lower than the top surface of the microwave transmitting plate by a distance of 66.5 mm.

Boundary condition: perfect conductor

Microwave frequency: 2.45 GHz

Input power: 2000 W

Microwave transmitting plate: SiO₂

Dielectric constant: SiO₂=4.2, Air=1.0

Pressure in the chamber: 13.3 Pa (100 mTorr)

Temperature: 500° C.

First, the electric field strength on the lower surface of the microwave transmitting plate was simulated when the microwave was supplied under the above conditions and radiated from the microwave transmitting plate.

When the microwave transmitting plate having the arch-type cross-section in FIG. 1 was used, as shown in FIG. 5A, an electric field strength distribution on a surface indicated by a line L1 along a lower surface of an arch portion of the microwave transmitting plate was obtained. Further, when the flat-type microwave transmitting plate was used, as shown in FIG. 5B, an electric field strength distribution on a lower surface (a line L2) of the microwave transmitting plate was obtained. Results therefrom were shown in FIG. 6A and FIG. 6B, respectively. In the case of the microwave transmitting plate having an arch-type cross-section, as shown in FIG. 6A, the electric field strength on the concave portion corresponding to the wafer W of the lower surface, which was the microwave radiating surface, was high and uniform, whereas in the case of the flat-type microwave transmitting plate, as shown in FIG. 6B, the electric field strength on an entire portion of the lower surface, which was the microwave radiating surface, including the portion corresponding to the wafer was low and non-uniform.

Next, the electric field strength in a vertical direction of the microwave transmitting plate was simulated.

When the microwave transmitting plate having an arch-type cross-section in FIG. 1 was used, as shown in FIG. 7A, the electric field strength on a portion from the upper surface of the microwave transmitting plate to a position being lower therefrom by a distance of 30 mm was obtained. Further, when the flat-type microwave transmitting plate was used, as shown in FIG. 7B, the electric field strength on a portion from the upper surface of the microwave transmitting plate to a position being lower therefrom by a distance of 30 mm was obtained. Results therefrom were shown in FIG. 8A and FIG. 8B, respectively. In the case of the microwave transmitting plate having an arch-type cross-section, as shown in FIG. 8A, the electric field strength and the uniformity were high as a whole, whereas in the case of the flat type microwave transmitting plate, as shown in FIG. 8B, the portions having the high electric field strength were sparsely present, and the electric field strength and the uniformity were low as a whole. This is because when the microwave was transmitted through the dielectric microwave transmitting plate, there was a portion where the reflected wave was generated.

From the simulation results, a power balance was obtained. When the microwave transmitting plate having an arch-type cross-section was used, among a total power of 2000 W, 1344 W was supplied into the chamber, 1301 W was absorbed in the plasma and 656 W was reflected. When the flat-type transmitting plate was used, among a total power of 2000 W, 234 W was supplied into the chamber, 216 W was absorbed in the plasma and 1766 W was reflected. From this result, it was confirmed that the microwave can be very effectively supplied according to the present invention.

Next, results of forming the plasma and executing the oxidizing process will be explained below.

The oxidizing plasma was formed by the microwave plasma processing apparatus using the planar antenna shown in FIG. 2 and the flat-type microwave transmitting plate and the microwave transmitting plate having an arch-type cross-section shown in FIG. 1, respectively, to obtain a distribution of the electron density in the plasma. Conditions were as follows: the pressure in the chamber was 133 Pa (1 Torr); the flow rate of Ar gas was 1500 mL/min (sccm); the flow rate of O₂ gas was 150 mL/min (sccm); and the microwave power was varied to 2000 W, 3000 W and 4000 W. The electron density is shown in FIG. 9 and FIG. 10. As shown in the drawings, it was confirmed that the uniformity of the electron density in the plasma was higher when using the microwave transmitting plate having an arch-type cross-section rather than using the flat-type microwave transmitting plate.

Next, the oxidizing process was executed by the same device. Conditions were as follows: the pressure in the chamber was 266 Pa (2 Torr); the flow rate of Ar gas was 2000 mL/min (sccm); the flow rate of O₂ gas was 200 mL/min (sccm); the microwave power was varied to 2000 W, 3000 W and 4000 W; and the temperature of the susceptor was 400° C. The oxidizing process was executed for 30 seconds to obtain the in-plane thickness distribution of the oxide film.

It was confirmed that when the flat-type microwave transmitting plate was used, an average thickness of the oxide film at 2000 W was 1.22 nm and the variation was 3.39% and the average thickness of the oxide film at 3000 W was 1.34 nm and the variation was 2.27%, whereas when the microwave transmitting plate having the arch-type cross-section in FIG. 1 was used, the average thickness of the oxide film at 2000 W was 1.16 nm and the variation was 0.90% and the average thickness of the oxide film at 3000 W was 1.26 nm and the variation was 1.02%. By combining the antenna in FIG. 2 and the microwave transmitting plate having an arch-type cross-section, the thickness distribution of the oxide film in the wafer surface became smaller.

Next, results of forming the plasma and executing the nitriding process will be explained below.

As discussed above, the nitriding plasma was formed by the microwave plasma processing apparatus using the planar antenna shown in FIG. 2 and the flat-type microwave transmitting plate and the microwave transmitting plate having the arch-type cross-section shown in FIG. 1, respectively, to obtain the distribution of the electron density in the plasma. Conditions were as follows: the pressure in the chamber was 6.7 Pa (50 mTorr); the flow rate of Ar gas was 1000 mL/min (sccm); the flow rate of N₂ gas was 40 mL/min (sccm); and the microwave power was varied to 600 W, 800 W, 1000 W, 1500 W and 2000 W. The electron density distribution is shown in FIG. 11 and FIG. 12. As shown in the drawings, since the nitriding plasma was plasma-generated at a lower pressure, the distribution thereof differs from that in the oxidizing plasma of a relatively high pressure. However, since the electron density distribution of the plasma tends to be non-uniform in the flat-type microwave transmitting plate as well, it was confirmed that the uniformity of the electron density in the plasma using the microwave transmitting plate having an arch-type cross-section was higher.

Next, the nitriding process was executed by the same device. Conditions were as follows: the pressure in the chamber was 6.7 Pa (50 mTorr); the flow rate of Ar gas was 1000 mL/min (sccm); the flow rate of N₂ gas was 40 mL/min (sccm); the microwave power was varied to 600 W, 800 W, 1000 W, 1500 W and 2000 W; and the temperature of the susceptor was 250° C. The nitriding process was executed for 30 seconds to obtain the in-plane thickness distribution of the nitride film.

When the flat-type microwave transmitting plate was used, the thickness of the nitride film became most uniform at 800 W and the average film thickness was 1.74 nm and the variation was 1.25%, whereas when the microwave transmitting plate having the arch-type cross-section in FIG. 1 was used, the thickness of the nitride film became most uniform at 1500 W and the average film thickness was 2.02 nm and the variation was 0.62%. From these results, it was confirmed that by combining the antenna shown in FIG. 2 and the microwave transmitting plate having the arch-type cross-section, the thickness distribution of the nitride film in the wafer surface became smaller.

Next, another embodiment of the present invention will be explained below.

FIG. 13 is a partial cross-sectional view of a microwave plasma processing apparatus in another embodiment of the present invention. As shown in FIG. 13, the microwave transmitting plate 28 has a microwave transmitting surface at its lower surface in a concavo-convex shape. More specifically, as shown in a bottom view of FIG. 14, convex portions 28 a and concave portions 28 h are concentrically formed by turns.

According to such a configuration, the standing wave can be effectively prevented from being generated in an in-plane direction of the microwave transmitting plate 28. Further, by this concavo-convex shaped microwave transmitting plate 28, the uniformity of the microwave to be radiated can be enhanced and the microwave can be effectively radiated.

Further, the convex portions and the concave portions are not necessarily concentrically arranged, but may be arranged in various ways.

Next, another embodiment of the present invention will be explained.

FIG. 15 is a partial cross-sectional view of a microwave plasma processing apparatus in another embodiment of the present invention. As shown in FIG. 15, the microwave transmitting plate 28 is provided with annular projections 28 i at its outer side end. The annular projections 28 i are projected downwardly from the microwave radiating surface.

By doing so, the plasma generated in the chamber 1 can be restrained by the projections 28 i from spreading outwardly, so that damage to the members such as the support portion 27 or abnormal discharge can be effectively prevented.

The present invention is not limited to the above embodiments and may include various modifications. For example, although the above embodiments illustrate the cases of applying the present invention to the oxidizing process and the nitriding process, the present invention is not limited thereto but may be applied to other surface processes. Further, the present invention is not limited to such surface processes, but may be applied to other plasma processes such as etching, resist ashing or CVD. Although the semiconductor wafer is used in the above embodiments as the workpiece, the present invention is not limited thereto but may be applied to other workpieces such as a flat panel display (FPD) substrate. 

1-14. (canceled)
 15. A microwave plasma processing apparatus for forming a plasma of a process gas by a microwave and executing a plasma process to a workpiece by the plasma, comprising: a chamber in which the workpiece is housed; a placing table for placing the workpiece in the chamber; a microwave generating source for generating a microwave; a waveguide for guiding the microwave generated from the microwave generating source toward the chamber; a planar antenna made of a conductive material for radiating the microwave guided by the waveguide toward the chamber; a microwave transmitting plate made of a dielectric material, the microwave transmitting plate defining a top wall of the chamber and transmitting the microwave that has passed through microwave radiating holes of the planar antenna; and a process gas introducing unit for introducing the process gas into the chamber via a pipe; wherein when a surface of the planar antenna is concentrically divided into a central region, an outer circumferential region and a middle region therebetween, a plurality of the microwave radiating holes are formed in the central region and the outer circumferential region and no microwave radiating hole is formed in the middle region; wherein a plurality of pairs of the microwave radiating holes are concentrically arranged in the central region and the outer circumferential region, the pair of the microwave radiating holes comprising a first microwave transmitting hole formed in an inner side and a second microwave radiating hole formed in an outer side, and the first and the second transmitting holes being disposed in different directions from each other; and wherein a concave portion is formed in a lower surface of the microwave transmitting plate; the concave portion has an arch-type cross-section; a portion of the concave portion corresponding to the workpiece is flat; and at least a portion of the first microwave radiating hole of the pair of the microwave radiating holes formed in the outer circumferential region is arranged so as to be engaged with the concave portion.
 16. The microwave plasma processing apparatus of claim 15, wherein the pair of the microwave radiating holes is formed such that ends in longitudinal directions of the first microwave radiating hole and the second microwave radiating hole are close to each other and the other ends are spaced from each other.
 17. The microwave plasma processing apparatus of claim 16, wherein an angle formed between the longitudinal directions of the first microwave radiating hole and the second microwave radiating hole ranges from 80° to 100°.
 18. The microwave plasma processing apparatus of claim 15, wherein a length along the longitudinal direction of the microwave radiating hole formed in the central region is shorter than a length along the longitudinal direction of the microwave radiating hole formed in the outer circumferential region.
 19. The microwave plasma processing apparatus of claim 15, wherein the concave portion is formed to be larger than a diameter of the workpiece.
 20. The microwave plasma processing apparatus of claim 15, wherein a lower surface of the microwave transmitting plate has annular projections in its periphery projected downwardly.
 21. A microwave plasma processing apparatus for forming a plasma of a process gas by a microwave and executing a plasma process to a workpiece by the plasma, comprising: a chamber in which the workpiece is housed; a placing table for placing the workpiece in the chamber; a microwave generating source for generating a microwave; a waveguide for guiding the microwave generated from the microwave generating source toward the chamber; a planar antenna made of a conductive material for radiating the microwave guided by the waveguide toward the chamber; a microwave transmitting plate made of a dielectric material, the microwave transmitting plate defining a top wall of the chamber and transmitting the microwave that has passed through microwave radiating holes of the planar antenna; and a process gas introducing unit for introducing the process gas into the chamber via pipes; wherein when a surface of the planar antenna is concentrically divided into a central region, an outer circumferential region and a middle region therebetween, a plurality of the microwave radiating holes are formed in the central region and the outer circumferential region and no microwave radiating hole is formed in the middle region; wherein a plurality of pairs of the microwave radiating holes are concentrically arranged in the central region and the outer circumferential region, the pair of the microwave radiating holes comprising a first microwave radiating hole formed in an inner side and a second microwave radiating hole formed in an outer side, and the first and the second microwave radiating holes being disposed in different directions from each other; and wherein a lower surface of the microwave transmitting plate is formed in a concavo-convex shape.
 22. The microwave plasma processing apparatus of claim 21, wherein the pair of the microwave radiating holes is formed such that ends in longitudinal directions of the first microwave radiating hole and the second microwave radiating hole are close to each other and the other ends are spaced from each other.
 23. The microwave plasma processing apparatus of claim 22, wherein an angle formed between the longitudinal directions of the first microwave radiating hole and the second microwave radiating hole ranges from 80° to 100°.
 24. The microwave plasma processing apparatus of claim 21, wherein a length along the longitudinal direction of the microwave radiating hole formed in the central region is shorter than a length along the longitudinal direction of the microwave radiating hole formed in the outer circumferential region.
 25. The microwave plasma processing apparatus of claim 21, wherein a lower surface of the microwave transmitting plate has convex portions and concave portions concentrically arranged by turns.
 26. The microwave plasma processing apparatus of claim 21, wherein a lower surface of the microwave transmitting plate has annular projections in its periphery projected downwardly.
 27. The microwave plasma processing apparatus of claim 15, wherein a height of a portion of the microwave transmitting plate corresponding to the concave portion ranges from 10 to 30 mm.
 28. The microwave plasma processing apparatus of claim 15, wherein a height of the concave portion ranges from 15 to 25 mm.
 29. The microwave plasma processing apparatus of claim 15, wherein when a distance between a center point of the first microwave radiating hole in the central region and a center of the planar antenna is set as “1,” a distance between a center point of the first microwave radiating hole in the outer region and the center of the planar antenna ranges from 2 to
 4. 30. A microwave plasma processing apparatus for forming a plasma of a process gas by a microwave and executing a plasma process to a workpiece by the plasma, comprising: a chamber in which the workpiece is housed; a placing table for placing the workpiece in the chamber; a microwave generating source for generating a microwave; a waveguide for guiding the microwave generated from the microwave generating source toward the chamber; a planar antenna made of a conductive material for radiating the microwave guided by the waveguide toward the chamber; a microwave transmitting plate made of a dielectric material, the microwave transmitting plate defining a top wall of the chamber and transmitting the microwave that has passed through microwave radiating holes of the planar antenna; and a process gas introducing unit for introducing the process gas into the chamber via pipes, wherein when a surface of the planar antenna is concentrically divided into a central region, an outer circumferential region and a middle region therebetween, a plurality of the microwave radiating holes are formed in the central region and the outer circumferential region and no microwave radiating hole is formed in the middle region; wherein a plurality of pairs of the microwave radiating holes are concentrically arranged in the central region and the outer circumferential region, the pair of the microwave radiating holes comprising a first microwave radiating hole formed in an inner side and a second microwave radiating hole formed in an outer side, and the first and the second microwave radiating holes being disposed in different directions from each other; wherein when a distance between a center point of the first microwave radiating hole in the central region and a center of the planar antenna is set as “1,” a distance between a center point of the first microwave radiating hole in the outer region and the center of the planar antenna ranges from 2 to 4; and wherein a lower surface of the microwave transmitting plate has a concave portion having an arch-type cross-section and a portion of the concave portion corresponding to the workpiece is flat. 